MN-FLT-OH-201
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Nuisance Illumination of the COWL VALVE Lights
GOT-7
Flight Crew Operations Manual Bulletin
for
Gol Linhas Aereas S.A.
Number:
GOT
-
7
IssueDate:
April 4, 2018
Subject:
Nuisance Illumination of the COWL VALVE Lights
Reason:
This bulletin informs flight crews of nuisance illumination of the engine
anti-ice COWL VALVE lights when using engine anti-ice at altitudes
below FL230.
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
Background Information
During 737-8 flight tests, nuisance illumination of the amber COWL VALVE
light(s) occurred when engine anti-ice was used at altitudes below FL230.
Depending on bleed air demands, the high stage valve modulates open to
maintain adequate bleed air pressure. If the engine anti-ice is selected ON as the
high stage valve modulates, a transient low pressure can occur which can cause
the COWL VALVE light(s) to illuminate along with the master caution lights
and the amber ANTI-ICE light on the system annunciator panel.
The cause for the illumination of the COWL VALVE light(s) is that the pressure
switch senses a transient bleed air pressure drop downstream of the cowl anti-ice
valve. It is important to note that even though the COWL VALVE light(s) can
illuminate for approximately 15 seconds, sufficient bleed air pressure is available
to provide engine anti-ice protection.
This anomaly affects 737-7/-8/-9 airplanes prior to Line Number 7000. For these
airplanes Boeing will communicate appropriate modification instructions as soon
as they become available.
Information in this bulletin is recommended by The Boeing Company, but may not be FAA approved
at the time of writing. In the event of conflict with the FAA approved Airplane Flight Manual
(AFM), the AFM shall supersede. The Boeing Company regards the information or procedures
described herein as having a direct or indirect bearing on the safe operation of this model airplane.
March 1, 2021